In the fields of medicine, pharmaceutical production, and food processing there is a critical need for sterilization to protect against the danger of harmful microorganisms. Most of the sterilization methods currently in use require the sterilizing agent to systemically permeate the article being sterilized. These methods include heat sterilization, where the object to be sterilized is subjected to heat and pressure, such as in an autoclave. The heat and pressure penetrates though the object being sterilized and after a sufficient time will kill the harmful microorganisms. Gases such as hydrogen peroxide or ethylene oxide have also been used to sterilize objects. For the complete sterilization of an object, the gas must permeate the entire object. An alternate sterilization method uses ionizing radiation, such as gamma-rays, x-rays, or energetic electrons for sterilization.
There are a number of target objects where exposure of the object to ionizing radiation would cause some deleterious effect on the target object. Examples include objects which would melt or degrade under heat sterilization, products that would degrade or react with chemical sterilizing agents, and materials that would be harmfully altered by exposure to high energy radiation, particularly ionizing radiation. It has previously been recognized that by confining ionizing radiation to the surface of a target object, the deleterious effect will not occur. On the other hand, most ionizing radiation is created by powerful beam generators, such as accelerators, and so a beam of ionizing radiation is inherently penetrating.
In U.S. Pat. No. 4,801,427 A. Jacob teaches a process for dry sterilization of medical devices subjected to an electrical discharge in a gaseous atmosphere to produce an active plasma. In one embodiment, Jacob teaches placement of articles on a conveyor belt which carries articles into an atmospheric pressure corona discharge gap operated in ambient air. The plasma is formed by a discharge between the grounded conveyor belt, acting as a cathode, and multiple needle-like nozzles, acting as anodes, which disperse a gas to be ionized, which may be an oxidizing gas such as oxygen or a reducing gas such as hydrogen. U.S. Pat. No. 5,200,158, also to A. Jacob teaches sterilization by exposure of an object to a gas plasma created by an electrical discharge in a sub-atmospheric gaseous atmosphere. Hydrogen, oxygen, nitrogen, and inert gasses are all taught as possible gasses to use in forming the plasma.
In contradistinction to the high energy approach of Jacob, U.S. Pat. No. 3,780,308 to S. Nablo teaches surface sterilization of objects using low energy electrons, even though a relatively high energy starting point is present. One of the advantages of low energy electrons is that bulk properties essential to the mechanics of the material sterilized are not affected. Nablo expanded upon his idea in U.S. Pat. No. 4,652,763 which teaches use of an electron beam producing electrons with energies that penetrate an outer layer but with insufficient energy to pierce an inner layer of target material.
A number of patents teach use of a gas plasma to effect surface sterilization. Fraser et al., in U.S. Pat. No. 3,948,601 teaches use of a continuous flow gas plasma supplied at very low pressure in a chamber with a target object to be sterilized. Cool plasma from a gas such as argon is continuously produced by exposure to a radio-frequency field.
One of the problems encountered in prior art sterilization devices involves three dimensional structures, such as vials, cuvettes and hoses. Sometimes such structures have contours which create shadows for a beam of ionizing radiation nor even a diffuse discharge such that reactive electrons or ions do not reach the contours and so there is little sterilization in such regions. One solution would be to rotate or otherwise turn the object being sterilized.
An object of the invention was to devise a sterilization apparatus for medical equipment and the like, having three dimensional structure, with full sterilization of contoured regions, using ionizing radiation, but not deleteriously effecting the target substance. Another object of the invention was to devise a sterilization apparatus which is more efficient than sterilization apparatus of the prior art.